1. Technical Field
The invention relates to a polymerizable compound having four groups that can be polymerized by light or heat, and a liquid crystal composition including the polymerizable compound. The invention also relates to a liquid crystal display device in which the orientation of liquid crystal molecules is fixed by sealing the liquid crystal composition between substrates, and then polymerizing the polymerizable compound while a voltage applied to the substrates is adjusted.
2. Technical Background
A liquid crystal display device utilizes optical anisotropy, dielectric anisotropy and so forth of liquid crystal molecules in a liquid crystal composition. A classification based on the operating mode for liquid crystal molecules includes a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a fringe field switching (FFS) mode and a vertical alignment (VA) mode.
A liquid crystal display device having a mode in which a polymer is used in combination with a liquid crystal composition is known. The mode is, for example, a polymer sustained alignment (PSA) mode or a polymer stabilized (PS) mode. Ina liquid crystal display device having this mode, a liquid crystal composition to which a polymerizable compound is added is poured into a display device. A polymer is formed in the liquid crystal composition by the irradiation with ultraviolet light which polymerizes the polymerizable compound, while a voltage is applied between electrodes. With this method, a liquid crystal display device is obtained in which the response time is decreased and the image burn-in is improved.
This method can be applied to a variety of operating modes of liquid crystal display devices, and modes such as PS-TN, PS-IPS, PS-FFS, PSA-VA and PSA-OCB are known. A polymerizable compound used for these kinds of modes seems to have a high ability to orient liquid crystal molecules, but its solubility in a liquid crystal composition is not reported to be high. Improvement of the solubility in a liquid crystal composition has been tried until now, but there is a tendency that the polymerization reactivity is decreased as the solubility increases. Thus, the development of a polymerizable compound having a suitable balance between the solubility and the polymerization reactivity has been expected.